High-temperature bimetal

ABSTRACT

A high-temperature bimetal capable of being inhibited from considerably shifting from an original position when the temperature has fallen to an ordinary temperature is provided. This high-temperature bimetal (1) includes a high thermal expansion layer (2) made of austenitic stainless steel and a low thermal expansion layer (3) made of a thermosensitive magnetic metal having a Curie point and bonded to the high thermal expansion layer. The high-temperature bimetal is employed over both a high temperature range of not less than the Curie point and a low temperature range of less than the Curie point, while an upper limit of operating temperatures in the high temperature range of not less than the Curie point is at least 500° C.

TECHNICAL FIELD

The present invention relates to a high-temperature bimetal, and moreparticularly, it relates to a high-temperature bimetal including a highthermal expansion layer and a low thermal expansion layer.

BACKGROUND ART

In general, a high-temperature bimetal including a high thermalexpansion layer and a low thermal expansion layer is known (refer toPatent Document 1, for example).

The aforementioned Patent Document 1 discloses a high-temperaturebimetal including a sprayed layer (high thermal expansion layer) made ofa 16Cr-5Al-0.3Y—Fe alloy containing 16 mass % of Cr, 5 mass % of Al, 0.3mass % of Y, and Fe and a plurality of W lines (low thermal expansionlayer) arranged parallel to each other at regular intervals, deformed bybending in response to temperature changes. The plurality of W lines ofthe high-temperature bimetal disclosed in this Patent Document 1 areembedded in the sprayed layer on the side closer to the upper surface ina state where the same are separated from each other with the samedistance from the upper surface of the sprayed layer toward an innerportion. The high-temperature bimetal disclosed in this Patent Document1 has a highest acceptable temperature (an upper limit of an operatingtemperature range) of 1200° C. and a bending coefficient of 5 to6×10⁻⁶/K. The high-temperature bimetal disclosed in this Patent Document1 conceivably has a substantially constant bending coefficient (5 to6×10⁻⁶/K) in the whole operating temperature range.

PRIOR ART DOCUMENT Patent Document

Patent Document 1: Japanese Patent Laying-Open No. 61-25090

SUMMARY OF THE INVENTION Problems to be Solved by the Invention

However, the high-temperature bimetal disclosed in the aforementionedPatent Document 1 conceivably has a substantially constant bendingcoefficient (5 to 6×10⁻⁶/K) in the whole operating temperature range.The mode of use of a bimetal include a mode where a high-temperaturebimetal comes into contact with a stopper member for limitingdeformation due to bending of the high-temperature bimetal within adefinite range at a set temperature smaller than the highest acceptabletemperature (1200° C.). In this case, the stopper member inhibits thedeformation of the high-temperature bimetal in a high temperature rangebetween the set temperature and the highest acceptable temperature. Atthis time, the high-temperature bimetal having a substantially constantbending coefficient in the whole operating temperature range as in theaforementioned Patent Document 1 has a large bending coefficient overthe whole range of a low temperature range and the high temperaturerange, and hence thermal stress is easily accumulated in thehigh-temperature bimetal. Therefore, if the temperature falls to anordinary temperature again after the temperature rises from the ordinarytemperature to the vicinity of the highest acceptable temperature, thehigh-temperature bimetal disadvantageously considerably shifts from anoriginal position at the ordinary temperature.

The present invention has been proposed in order to solve theaforementioned problem, and an object of the present invention is toprovide a high-temperature bimetal capable of being inhibited fromconsiderably shifting from an original position when the temperature hasfallen to an ordinary temperature.

Means for Solving the Problems and Effect of the Invention

A high-temperature bimetal according to an aspect of the presentinvention includes a high thermal expansion layer made of austeniticstainless steel and a low thermal expansion layer made of athermosensitive magnetic metal having a Curie point and bonded to thehigh thermal expansion layer. The high-temperature bimetal is employedover both a high temperature range of not less than the Curie point anda low temperature range of less than the Curie point, while an upperlimit of operating temperatures in the high temperature range of notless than the Curie point is at least 500° C.

As hereinabove described, the high-temperature bimetal according to theaspect of the present invention has the low thermal expansion layer madeof the thermosensitive magnetic metal having the Curie point and isemployed over both the high temperature range of not less than the Curiepoint and the low temperature range of less than the Curie point,whereby a thermal expansion coefficient of the thermosensitive magneticmetal in the high temperature range of not less than the Curie point islarger than a thermal expansion coefficient of the thermosensitivemagnetic metal in the low temperature range of less than the Curiepoint. Therefore, a difference between a thermal expansion coefficientof the high thermal expansion layer in the high temperature range andthe thermal expansion coefficient of the low thermal expansion layer inthe high temperature range can be rendered smaller than a differencebetween a thermal expansion coefficient of the high thermal expansionlayer in the low temperature range and the thermal expansion coefficientof the low thermal expansion layer in the low temperature range. Thus,in the high-temperature bimetal of the present invention, deformationdue to bending in the high temperature range is small compared withdeformation due to bending in the low temperature range, and hence adisplacement of the deformation due to bending of the high-temperaturebimetal in the high temperature range of not less than the Curie pointcan be rendered smaller than a displacement of the deformation due tobending of the high-temperature bimetal in the low temperature range ofless than the Curie point. Therefore, accumulation of thermal stress inthe high-temperature bimetal can be inhibited in the high temperaturerange of not less than the Curie point, and hence thermal stress can behardly accumulated in the high-temperature bimetal. Consequently, thehigh-temperature bimetal capable of being inhibited from considerablyshifting from an original position when the temperature has fallen tothe ordinary temperature can be provided.

Preferably in the aforementioned high-temperature bimetal according tothe aspect, a bending coefficient in the high temperature range of notless than the Curie point is smaller than a bending coefficient in thelow temperature range of less than the Curie point, when in use.According to this structure, the deformation due to bending of thehigh-temperature bimetal in the high temperature range of not less thanthe Curie point is smaller than the deformation due to bending of thehigh-temperature bimetal in the low temperature range of less than theCurie point, and hence accumulation of thermal stress in thehigh-temperature bimetal can be easily inhibited in the high temperaturerange of not less than the Curie point.

Preferably in the aforementioned high-temperature bimetal according tothe aspect, the Curie point of the thermosensitive magnetic metal of thelow thermal expansion layer is at least 100° C. and not more than 400°C., and the upper limit of the operating temperatures in the hightemperature range of not less than the Curie point is at least 500° C.and not more than 700° C. According to this structure, the usefulhigh-temperature bimetal can be obtained when it is desired to renderthermal expansion small in a temperature range of at least a temperatureincluded in at least about 100° C. and not more than 400° C. Further,the high-temperature bimetal having an upper limit of operatingtemperatures in a temperature range of at least 500° C. and not morethan 700° C. is employed, whereby the high-temperature bimetal capableof being employed until a temperature included in at least 500° C. andnot more than 700° C. and only slightly shifting from the originalposition when the temperature has fallen can be obtained.

Preferably in this case, a range of the operating temperatures in thehigh temperature range of not less than the Curie point is larger than arange of operating temperatures in the low temperature range of lessthan the Curie point. According to this structure, a temperature rangeof the high temperature range of not less than the Curie point, in whichthe displacement of the high-temperature bimetal is small, can berendered larger than a temperature range of the low temperature range ofless than the Curie point, in which the displacement of thehigh-temperature bimetal is large. Consequently, accumulation of thermalstress in the high-temperature bimetal can be further inhibited in thehigh temperature range of not less than the Curie point.

Preferably in the aforementioned high-temperature bimetal according tothe aspect, the thermosensitive magnetic metal of the low thermalexpansion layer is a Ni—Fe alloy. According to this structure, thethermosensitive magnetic metal having the Curie point can be easilyobtained.

Preferably in this case, the thermosensitive magnetic metal of the lowthermal expansion layer is a Ni—Fe alloy containing at least 32 mass %and not more than 45 mass % of Ni. According to this structure, thehigh-temperature bimetal having the Curie point of at least 100° C. andnot more than 400° C. can be easily obtained.

Preferably in the aforementioned high-temperature bimetal in which thethermosensitive magnetic metal is the Ni—Fe alloy containing at least 32mass % and not more than 45 mass % of Ni, the thermosensitive magneticmetal of the low thermal expansion layer is formed by adding at leastone of Nb, Cr, Al, Si, and Ti to the Ni—Fe alloy. According to thisstructure, the high-temperature bimetal in which oxidation resistance isfurther provided to the thermosensitive magnetic metal with the Curiepoint of at least 100° C. and not more than 400° C. can be obtained.

Preferably in the aforementioned high-temperature bimetal in which thethermosensitive magnetic metal is formed by adding at least one of Nb,Cr, Al, Si, and Ti to the Ni—Fe alloy, the thermosensitive magneticmetal of the low thermal expansion layer is formed by adding at least 2mass % and not more than 8 mass % of Nb to the Ni—Fe alloy. According tothis structure, at least 2 mass % of Nb is added to the Ni—Fe alloy,whereby such sufficient oxidation resistance that a problem is notcaused even if the temperature rises to the upper limit of the operatingtemperatures of the high-temperature bimetal can be provided to thethermosensitive magnetic metal. Further, a reduction in the workabilityof the thermosensitive magnetic metal due to an excessive increase inthe strength of the thermosensitive magnetic metal by adding more than 8mass % of Nb to the Ni—Fe alloy can be inhibited.

Preferably in the aforementioned high-temperature bimetal in which thethermosensitive magnetic metal is formed by adding at least 2 mass % andnot more than 8 mass % of Nb to the Ni—Fe alloy, the thermosensitivemagnetic metal of the low thermal expansion layer is formed by adding 6mass % of Nb to a Ni—Fe alloy containing 36 mass % of Ni. According tothis structure, the high-temperature bimetal being oxidation-resistantenough not to cause a problem even if the temperature rises to the upperlimit of the operating temperatures of the high-temperature bimetal andhaving the low thermal expansion layer made of the thermosensitivemagnetic metal capable of inhibiting a reduction in workability can beobtained.

Preferably in the aforementioned high-temperature bimetal in which thethermosensitive magnetic metal is formed by adding at least 2 mass % andnot more than 8 mass % of Nb to the Ni—Fe alloy, the thermosensitivemagnetic metal of the low thermal expansion layer is formed by adding 2mass % of Nb to a Ni—Fe alloy containing 36 mass % of Ni. According tothis structure, the high-temperature bimetal being oxidation-resistantenough not to cause a problem even if the temperature rises to the upperlimit of the operating temperatures of the high-temperature bimetal andhaving the low thermal expansion layer made of the thermosensitivemagnetic metal capable of inhibiting a reduction in workability can beobtained.

Preferably in the aforementioned high-temperature bimetal in which thethermosensitive magnetic metal is formed by adding at least one of Nb,Cr, Al, Si, and Ti to the Ni—Fe alloy, the thermosensitive magneticmetal of the low thermal expansion layer is formed by adding at least 2mass % and not more than 13 mass % of Cr to the Ni—Fe alloy. Accordingto this structure, at least 2 mass % of Cr is added to the Ni—Fe alloy,whereby such sufficient oxidation resistance that a problem is notcaused even if the temperature rises to the upper limit of the operatingtemperatures of the high-temperature bimetal can be provided to thethermosensitive magnetic metal. Further, an excessive increase in thethermal expansion coefficient of the low thermal expansion layer byadding more than 13 mass % of Cr to the Ni—Fe alloy can be inhibited.

Preferably in the aforementioned high-temperature bimetal in which thethermosensitive magnetic metal is formed by adding at least 2 mass % andnot more than 13 mass % of Cr to the Ni—Fe alloy, the thermosensitivemagnetic-metal of the low thermal expansion layer is formed by adding 10mass % of Cr to a Ni—Fe alloy containing 40 mass % of Ni. According tothis structure, the high-temperature bimetal being oxidation-resistantenough not to cause a problem even if the temperature rises to the upperlimit of the operating temperatures of the high-temperature bimetal andhaving the low thermal expansion layer made of the thermosensitivemagnetic metal capable of inhibiting an increase in the thermalexpansion coefficient can be obtained.

Preferably in the aforementioned high-temperature bimetal according tothe aspect, a thickness of the low thermal expansion layer is largerthan a thickness of the high thermal expansion layer. According to thisstructure, the high-temperature bimetal having a large bendingcoefficient in the low temperature range of less than the Curie pointcan be easily obtained.

Preferably in the aforementioned high-temperature bimetal according tothe aspect, a total thickness of the high thermal expansion layer andthe low thermal expansion layer increased by oxidation of the highthermal expansion layer and the low thermal expansion layer resultingfrom a rise in a temperature to the upper limit of the operatingtemperatures in the high temperature range of not less than the Curiepoint is not more than 1% of a total thickness of the high thermalexpansion layer and the low thermal expansion layer before the oxidationof the high thermal expansion layer and the low thermal expansion layer.According to this structure, the property (bending coefficient or thelike) of the high-temperature bimetal can be inhibited from changing tosuch an extent that a practical problem is caused by an increase in thetotal thickness of the high thermal expansion layer and the low thermalexpansion layer by more than 1% due to the oxidation.

Preferably in this case, a total of mass increase per cubic centimeterof the high thermal expansion layer and the low thermal expansion layerincreased by the oxidation is not more than 1.5 mg. According to thisstructure, it can be easily confirmed whether or not the total thicknessof the high thermal expansion layer and the low thermal expansion layerhas increased by more than 1% due to the oxidation.

Preferably in the aforementioned high-temperature bimetal according tothe aspect, a thermal expansion coefficient of the low thermal expansionlayer in the high temperature range of not less than the Curie point issmaller than a thermal expansion coefficient of the high thermalexpansion layer and larger than a thermal expansion coefficient of thelow thermal expansion layer in the low temperature range of less thanthe Curie point. According to this structure, the high-temperaturebimetal can be inhibited from being deformed to the side closer to thehigh thermal expansion layer in the high temperature range of not lessthan the Curie point by having the low thermal expansion layer, thethermal expansion coefficient of which in the high temperature range ofnot less than the Curie point is equal to or larger than the thermalexpansion coefficient of the high thermal expansion layer. Further, thethermal expansion coefficient of the low thermal expansion layer in thehigh temperature range of not less than the Curie point is larger thanthe thermal expansion coefficient of the low thermal expansion layer inthe low temperature range of less than the Curie point, whereby thedeformation due to bending of the high-temperature bimetal in the lowtemperature range of less than the Curie point can be inhibited fromdecrease.

Preferably in this case, the thermal expansion coefficient of the lowthermal expansion layer in the high temperature range of not less thanthe Curie point is at least 70% and less than 100% of the thermalexpansion coefficient of the high thermal expansion layer. According tothis structure, the high-temperature bimetal can be inhibited from beingdeformed to the side closer to the high thermal expansion layer in thehigh temperature range, and the deformation due to bending of thehigh-temperature bimetal in the high temperature range can be inhibitedfrom increase due to a significant difference between the thermalexpansion coefficient of the high thermal expansion layer and thethermal expansion coefficient of the low thermal expansion layer in thehigh temperature range.

Preferably in the aforementioned high-temperature bimetal in which thethermal expansion coefficient of the low thermal expansion layer in thehigh temperature range is larger than the thermal expansion coefficientof the low thermal expansion layer in the low temperature range, thethermal expansion coefficient of the low thermal expansion layer in thehigh temperature range of not less than the Curie point is at leasttwice the thermal expansion coefficient of the low thermal expansionlayer in the low temperature range of less than the Curie point.According to this structure, the deformation due to bending of thehigh-temperature bimetal in the low temperature range of less than theCurie point can be further inhibited from decrease.

Preferably in the aforementioned high-temperature bimetal according tothe aspect, a thermal expansion coefficient of the low thermal expansionlayer in the low temperature range of less than the Curie point is notmore than 50% of a thermal expansion coefficient of the high thermalexpansion layer. According to this structure, the difference between thethermal expansion coefficient of the high thermal expansion layer in thelow temperature range and the thermal expansion coefficient of the lowthermal expansion layer in the low temperature range can be renderedlarge, and hence the high-temperature bimetal in the low temperaturerange can be more highly deformed by bending.

Preferably in the aforementioned high-temperature bimetal according tothe aspect, a first end portion of the low thermal expansion layer isfixed, and a vicinity of a second end portion of the low thermalexpansion layer comes into contact with a fixed stopper member in thehigh temperature range of not less than the Curie point. According tothis structure, the low thermal expansion layer comes into contact withthe stopper member in the high temperature range of not less than theCurie point in which accumulation of thermal stress in thehigh-temperature bimetal is inhibited, and hence thermal stressresulting from contact with the stopper member can be hardly accumulatedin the high-temperature bimetal.

Preferably in this case, the vicinity of the second end portion of thelow thermal expansion layer comes into contact with the stopper memberat a temperature in the high temperature range of not less than theCurie point and close to the Curie point. According to this structure,the low thermal expansion layer comes into contact with the stoppermember at a temperature close to the Curie point, and hence a statewhere the thermal stress resulting from contact with the stopper memberis hardly accumulated in the high-temperature bimetal is available overa wide temperature range.

BRIEF DESCRIPTION OF THE DRAWINGS

[FIG. 1] A diagram showing a high-temperature bimetal in an initialstate according to each of first to third embodiments of the presentinvention.

[FIG. 2] A diagram showing the high-temperature bimetal in a state wherethe temperature has risen from the state shown in FIG. 1 to reach a settemperature.

[FIG. 3] A diagram showing the high-temperature bimetal in a state wherethe temperature has risen from the state shown in FIG. 2 to reach ahighest acceptable temperature.

[FIG. 4] A diagram showing the high-temperature bimetal in a state wherethe temperature has fallen from the state shown in FIG. 3 to return toan ordinary temperature.

[FIG. 5] A diagram for illustrating an initial state of measurement of adisplacement conducted in order to confirm the effects of the presentinvention.

[FIG. 6] A diagram for illustrating a state of deformation due tobending of the measurement of a displacement conducted in order toconfirm the effects of the present invention.

[FIG. 7] A table showing the Curie points and the thermal expansioncoefficients of Examples 1, 2, and 3 and a comparative example 1employed in order to confirm the effects of the present invention.

[FIG. 8] A graph showing results of the measurement of a displacementconducted in order to confirm the effects of the present invention.

[FIG. 9] A table showing the results of the measurement of adisplacement conducted in order to confirm the effects of the presentinvention.

[FIG. 10] A table showing bending coefficients obtained from themeasurement of a displacement conducted in order to confirm,the effectsof the present invention.

[FIG. 11] A graph showing results of measurement of an oxidation massincrease conducted in order to confirm the effects of the presentinvention.

MODES FOR CARRYING OUT THE INVENTION

Embodiments of the present invention are hereinafter described withreference to the drawings.

First Embodiment

The structure of a high-temperature bimetal 1 according to a firstembodiment of the present invention is now described with reference toFIG. 1.

The high-temperature bimetal 1 according to the first embodiment of thepresent invention is constituted by a two-layered cladding materialincluding a plate-like high thermal expansion layer 2 and a plate-likelow thermal expansion layer 3 bonded to the high thermal expansion layer2, as shown in FIG. 1. The high-temperature bimetal 1 has a thickness t1of about 0.2 mm.

The high-temperature bimetal 1 is formed not to be deformed by bendingat an ordinary temperature T1 (about 25° C.), which is an initial state.As an example of the mode of use of the high-temperature bimetal 1, inthe first embodiment, a first end of the high-temperature bimetal 1 isfixed with a fixing portion 4 when the high-temperature bimetal 1 isemployed in a prescribed device (not shown). Further, the prescribeddevice employing the high-temperature bimetal 1 is provided with astopper 5 for inhibiting excessive deformation of the high-temperaturebimetal 1 on the side closer to a second end of the high-temperaturebimetal 1 and the low thermal expansion layer 3. This stopper 5 isarranged to come into contact with the high-temperature bimetal 1 whenthe high-temperature bimetal 1 is deformed by bending at a prescribedset temperature T2. The stopper 5 is an example of the “stopper member”in the present invention.

According to the first embodiment, a lower limit of an operatingtemperature range in which the high-temperature bimetal 1 can beemployed is about −70° C., and an upper limit (highest acceptabletemperature T3) of the operating temperature range is about 700° C. Theupper limit of the operating temperature range of the high-temperaturebimetal 1 may simply be at least about 500° C. and is preferably atleast about 500° C. and not more than about 700° C.

The high thermal expansion layer 2 is made of a 18Cr-8Ni—Fe alloy(SUS304) containing about 18 mass % of Cr, about 8 mass % of Ni, Fe, andtrace unavoidable impurities. Fe is a basic constituent of the SUS304and occupies the balance other than Cr, Ni, and unavoidable impurities.The SUS304 of the high thermal expansion layer 2 is austenitic stainlesssteel and has a thermal expansion coefficient of about 17.3×10⁻⁶/K.

According to the first embodiment, the low thermal expansion layer 3 ismade of a 36Ni-6Nb—Fe alloy containing about 36 mass % of Ni, about 6mass % of Nb, Fe, and trace unavoidable impurities. Fe is a basicconstituent of the 36Ni-6Nb—Fe alloy and occupies the balance other thanNi, Nb, and unavoidable impurities. The 36Ni-6Nb—Fe alloy of the lowthermal expansion layer 3 is a thermosensitive magnetic metal having aCurie point of about 200° C. Thus, the Curie point (about 200° C.) ofthe 36Ni-6Nb—Fe alloy of the low thermal expansion layer 3 is includedin the operating temperature range of at least about −70° C. and notmore than about 700° C. in which the high-temperature bimetal 1 can beemployed. Thus, the high-temperature bimetal 1 according to the firstembodiment is formed to be employed over both a high temperature rangeof not less than the Curie point and a low temperature range of lessthan the Curie point. The “Curie point” denotes a temperature at whichthe thermosensitive magnetic metal changes from a ferromagnetic materialto a paramagnetic material when the temperature rises and a temperatureat which the thermosensitive magnetic metal changes from a paramagneticmaterial to a ferromagnetic material when the temperature falls.

In the high-temperature bimetal 1, an operating temperature range (about700° C.−about 200° C.=about 500° C.) of a high temperature range of atleast the Curie point (about 200° C.) and not more than about 700° C. islarger than an operating temperature range (about 200° C.−(about −70°C.)=about 270° C.) of a low temperature range of at least about −70° C.and less than the Curie point (about 200° C.)

The 36Ni-6Nb—Fe alloy of the low thermal expansion layer 3 is formed tohave a thermal expansion coefficient of about 4.1×10⁻⁶/K in the lowtemperature range of less than the Curie point (about 200° C.) and athermal expansion coefficient of about 15.8×10⁻⁶/K in the hightemperature range of not less than the Curie point. The 36Ni-6Nb—Fealloy of the low thermal expansion layer 3 is formed such that thethermal expansion coefficient (about 4.1×10⁻⁶/K) thereof in the lowtemperature range of less than the Curie point is smaller than thethermal expansion coefficient (about 15.8×10⁻⁶/K) thereof in the hightemperature range of not less than the Curie point. The thermalexpansion coefficient (about 15.8×10⁻⁶/K) of the low thermal expansionlayer 3 in the high temperature range is about 3.9 times the thermalexpansion coefficient (about 4.1×10⁻⁶/K) of the low thermal expansionlayer 3 in the low temperature range. The thermal expansion coefficientof the low thermal expansion layer 3 in the high temperature range ispreferably at least about twice the thermal expansion coefficient of thelow thermal expansion layer 3 in the low temperature range.

Thus, a difference (about 1.5×10⁻⁶/K) between the thermal expansioncoefficient (about 17.3×10⁻⁶/K) of the high thermal expansion layer 2 inthe high temperature range and the thermal expansion coefficient (about15.8×10⁻⁶/K) of the low thermal expansion layer 3 in the hightemperature range is smaller than a difference (about 13.2×10⁻⁶/K)between the thermal expansion coefficient (about 17.3×10⁻⁶/K) of thehigh thermal expansion layer 2 in the low temperature range and thethermal expansion coefficient (about 4.1×10⁻⁶/K) of the low thermalexpansion layer 3 in the low temperature range.

The thermal expansion coefficients (about 4.1×10⁻⁶/K and about15.8×10⁻⁶/K) of the 36Ni-6Nb—Fe alloy of the low thermal expansion layer3 in the low temperature range and the high temperature range aresmaller than the thermal expansion coefficient (about 17.3×10⁻⁶/K) ofthe SUS304 of the high thermal expansion layer 2. Specifically, thethermal expansion coefficient (about 4.1×10⁻⁶/K) of the 36Ni-6Nb—Fealloy of the low thermal expansion layer 3 in the low temperature rangeof less than the Curie point (about 200° C.) is about 24% of the thermalexpansion coefficient (about 17.3×10⁻⁶/K) of the SUS304 of the highthermal expansion layer 2. Further, the thermal expansion coefficient(about 15.8×10⁻⁶/K) of the 36Ni-6Nb—Fe alloy of the low thermalexpansion layer 3 in the high temperature range of not less than theCurie point is about 91% of the thermal expansion coefficient (about17.3×10⁻⁶/K) of the SUS304 of the high thermal expansion layer 2. Thethermal expansion coefficient of the low thermal expansion layer 3 inthe low temperature range is preferably not more than about 50% of thethermal expansion coefficient of the high thermal expansion layer 2, andthe thermal expansion coefficient of the low thermal expansion layer 3in the high temperature range is preferably at least about 70% and lessthan about 100% of the thermal expansion coefficient of the high thermalexpansion layer 2.

The high-temperature bimetal 1 has a bending coefficient K1 of about6.7×10⁻⁶/K in the low temperature range of less than the Curie point(about 200° C.) and a bending coefficient K2 of about 3.3×10⁻⁶/K in thehigh temperature range of not less than the Curie point. Thehigh-temperature bimetal 1 is formed such that the bending coefficientK2 (about 3.3×10⁻⁶/K) is smaller than the bending coefficient K1 (about6.7×10⁻⁶/K).

As shown in FIG. 1, the thickness t2 of the SUS304 of the high thermalexpansion layer 2 of the high-temperature bimetal 1 and the thickness t3of the 36Ni-6Nb—Fe alloy of the low thermal expansion layer 3 of thehigh-temperature bimetal 1 satisfy a relation: t2:t3=about 47:about 53.In other words, the proportion of the thickness t3 of the 36Ni-6Nb—Fealloy of the low thermal expansion layer 3 to the total thickness t1 ofthe high-temperature bimetal 1 is about 0.53, whereby the thickness t3of the 36Ni-6Nb—Fe alloy of the low thermal expansion layer 3 is largerthan the thickness t2 of the SUS304 of the high thermal expansion layer2.

The high-temperature bimetal 1 is formed such that the mass (oxidationmass increase) of the high-temperature bimetal 1 increased by oxidationof the high-temperature bimetal 1 (the high thermal expansion layer 2and the low thermal expansion layer 3) resulting from a rise in thetemperature to an upper limit (about 700° C.) of operating temperaturesin the high temperature range of not less than the Curie point (about200° C.) is not more than about 1.5 mg per cubic centimeter. If theoxidation mass increase is more than about 1.5 mg (acceptable value) percubic centimeter, an increase in the thickness of the high-temperaturebimetal 1 due to the oxidation is more than about 2 μm and exceeds about1% of the thickness (about 0.2 mm) of the high-temperature bimetal 1before the oxidation. Thus, if the oxidation mass increase is more thanabout 1.5 mg per cubic centimeter, the property (bending coefficient Kor the like) of the high-temperature bimetal 1 changes to such an extentthat a practical problem is caused.

The deformation due to bending of the high-temperature bimetal 1according to the first embodiment of the present invention is nowdescribed with reference to FIGS. 1 to 4.

As shown in FIG. 1, the high-temperature bimetal 1 is not deformed bybending in an initial state (ordinary temperature T1 (about 25° C.)). Ifthe temperature rises from that state, the high-temperature bimetal 1 isdeformed by bending to the side closer to the low thermal expansionlayer 3 thereby causing a displacement D (see FIG. 2). When thetemperature reaches the prescribed set temperature T2, the side of thehigh-temperature bimetal 1 closer to the low thermal expansion layer 3comes into contact with the stopper 5 provided on the prescribed deviceemploying the high-temperature bimetal 1, as shown in FIG. 2.

In the mode of use of the high-temperature bimetal 1 according to thefirst embodiment, the prescribed set temperature T2 is close to theCurie point (about 200° C.) of the low thermal expansion layer 3 of thehigh-temperature bimetal 1 and higher than the Curie point.

If the temperature further rises from a state where the side of thehigh-temperature bimetal 1 closer to the low thermal expansion layer 3and the stopper 5 come into contact with each other, thehigh-temperature bimetal 1 is attempted to be deformed by bending to theside closer to the low thermal expansion layer 3 with the rise in thetemperature while the stopper 5 restricts larger deformation than thedeformation due to bending at the prescribed set temperature T2 duringthe rise in the temperature from the prescribed set temperature T2 tothe highest acceptable temperature T3 (about 700° C.), as shown in FIG.3. Therefore, force is applied from the high-temperature bimetal 1 tothe stopper 5 while reaction force is applied from the stopper 5 to thehigh-temperature bimetal 1. This reaction force changes to thermalstress and is accumulated in the high-temperature bimetal 1.

According to the first embodiment, the bending coefficient K2 (about3.3×10⁻⁶/K) of the high-temperature bimetal 1 in the high temperaturerange of not less than the Curie point (about 200° C.) is smaller thanthe bending coefficient K1 (about 6.7×10⁻⁶/K) of the high-temperaturebimetal 1 in the low temperature range of less than the Curie point, andhence the deformation due to bending in the high temperature range ofnot less than the Curie point is smaller than the deformation due tobending in the low temperature range of less than the Curie point. Thus,the force applied from the high-temperature bimetal 1 to the stopper 5is small compared with force applied in a case where thehigh-temperature bimetal has only the bending coefficient K1 in the lowtemperature range of less than the Curie point (a case where thehigh-temperature bimetal has no Curie point and the bending coefficientK thereof is constant).

Thus, if the temperature falls from the highest acceptable temperatureT3 (about 700° C.) to return (decrease) to the ordinary temperature T1(about 25° C.), the deformation due to bending resulting from thethermal stress accumulated in the high-temperature bimetal 1 is smallcompared with deformation due to bending of a high-temperature bimetalaccording to a conventional example of the present invention having noCurie point, the bending coefficient K of which is constant (aconventional example indicated by a two-dot chain line in FIG. 4), asshown in FIG. 4. In other words, a shift of the high-temperature bimetal1 according to the first embodiment from an original position is smallcompared with a shift of the high-temperature bimetal according to theconventional example of the present invention from the originalposition.

A method for manufacturing the high-temperature bimetal 1 according tothe first embodiment of the present invention is now described withreference to FIG. 1.

Plate-like SUS304 having a thickness of about 1.5 mm and a plate-like36Ni-6Nb—Fe alloy having a thickness of about 1.7 mm arecold-pressure-bonded to each other at a rolling reduction of about 60.6%thereby forming a bimetal made of a two-layered cladding material havinga thickness of about 1.3 mm. Then, diffusion annealing is performedunder a hydrogen atmosphere at about 1050° C. for about three minutes.Thus, the bond strength between a high thermal expansion layer and a lowthermal expansion layer of the bimetal can be improved. Thereafter, thebimetal having a thickness of about 1.3 mm is cold-rolled to have athickness t1 (see FIG. 1) of about 0.2 mm. Thus, the high-temperaturebimetal 1 (see FIG. 1) according to the first embodiment is formed.

Also in the aforementioned pressure-bonding and rolling, the ratiobetween the thickness of the plate-like SUS304 and the thickness of theplate-like 36Ni-6Nb—Fe alloy remains unchanged. Thus, the thickness t2(see FIG.

1) of the high thermal expansion layer 2 made of the SUS304 and thethickness t3 (see FIG. 1) of the low thermal expansion layer 3 made ofthe 36Ni-6Nb—Fe alloy satisfy a relation: t2:t3=about 1.5:about1.7=about 47:about 53.

According to the first embodiment, as hereinabove described, the lowthermal expansion layer 3 is made of the 36Ni-6Nb—Fe alloy having theCurie point (about 200° C.), and the high-temperature bimetal 1 isemployed over both the high temperature range (at least about 200° C.and not more than about 700° C.) not less than the Curie point and thelow temperature range (at least about −70° C. and less than about 200°C.) less than the Curie point. Thus, the thermal expansion coefficient(about 15.8×10⁻⁶/K) of the 36Ni-6Nb—Fe alloy in the high temperaturerange of not less than the Curie point is larger than the thermalexpansion coefficient (about 4:1×10⁻⁶/K) of the 36Ni-6Nb—Fe alloy in thelow temperature range of less than the Curie point, and hence thedifference (about 1.5×10⁻⁶/K) between the thermal expansion coefficient(about 17.3×10⁻⁶/K) of the high thermal expansion layer 2 in the hightemperature range and the thermal expansion coefficient of the lowthermal expansion layer 3 in the high temperature range can be renderedsmaller than the difference (about 13.2×10⁻⁶/K) between the thermalexpansion coefficient of the high thermal expansion layer 2 in the lowtemperature range and the thermal expansion coefficient of the lowthermal expansion layer 3 in the low temperature range. Thus, thedeformation due to bending of the high-temperature bimetal 1 accordingto the first embodiment in the high temperature range is small comparedwith the deformation due to bending of the high-temperature bimetal 1according to the first embodiment in the low temperature range, andhence the displacement D of the deformation due to bending of thehigh-temperature bimetal 1 in the high temperature range of not lessthan the Curie point can be rendered smaller than the displacement D ofthe deformation due to bending of the high-temperature bimetal 1 in thelow temperature range of less than the Curie point. Therefore, even ifthe stopper 5 restricts the deformation of the high-temperature bimetal1 in the high temperature range (range from T2 to T3) including atemperature range higher than the vicinity of the Curie point,accumulation of thermal stress in the high-temperature bimetal 1 can beinhibited. Thus, thermal stress can be hardly accumulated inside.Consequently, the high-temperature bimetal 1 capable of being inhibitedfrom considerably shifting from an original position when thetemperature has fallen to the ordinary temperature can be provided.Further, the useful high-temperature bimetal 1 can be obtained when itis desired to render thermal expansion small in a temperature range ofat least about 200° C. while the high-temperature bimetal 1 capable ofbeing employed until about 700° C. and only slightly shifting from theoriginal position when the temperature has fallen can be easilyobtained.

According to the first embodiment, as hereinabove described, thehigh-temperature bimetal 1 is formed such that the bending coefficientK2 (about 3.3×10⁻⁶/K) of the high-temperature bimetal 1 in the hightemperature range of not less than the Curie point (about 200° C.) issmaller than the bending coefficient K1 (about 6.7×10⁻⁶/K) of thehigh-temperature bimetal 1 in the low temperature range of less than theCurie point, whereby the deformation due to bending of thehigh-temperature bimetal 1 in the high temperature range of not lessthan the Curie point is smaller than the deformation due to bending ofthe high-temperature bimetal 1 in the low temperature range of less thanthe Curie point. Thus, accumulation of thermal stress in thehigh-temperature bimetal 1 can be easily inhibited in the hightemperature range of not less than the Curie point.

According to the first embodiment, as hereinabove described, theoperating temperature range (about 500° C.) of the high temperaturerange of at least the Curie point (about 200° C.) and not more thanabout 700° C. is larger than the operating temperature range (about 270°C.) of the low temperature range of at least about −70° C. and less thanthe Curie point, whereby a temperature range of the high temperaturerange of not less than the Curie point, in which the displacement D ofthe high-temperature bimetal 1 is small, can be rendered larger than atemperature range of the low temperature range of less than the Curiepoint, in which the displacement D of the high-temperature bimetal 1 islarge. Consequently, accumulation of thermal stress in thehigh-temperature bimetal 1 can be further inhibited in the hightemperature range of not less than the Curie point.

According to the first embodiment, as hereinabove described, the lowthermal expansion layer 3 is made of the 36Ni-6Nb—Fe alloy containingabout 36 mass % of Ni, about 6 mass % of Nb, Fe, and trace unavoidableimpurities, whereby the high-temperature bimetal 1 including thethermosensitive magnetic metal having a Curie point of about 200° C. canbe obtained. Further, the high-temperature bimetal 1 beingoxidation-resistant enough not to cause a problem even if thetemperature rises to the upper limit (about 700° C.) of operatingtemperatures of the high-temperature bimetal 1 and including thethermosensitive magnetic metal capable of inhibiting a reduction inworkability can be obtained.

According to the first embodiment, as hereinabove described, thethickness t3 of the 36Ni-6Nb—Fe alloy of the low thermal expansion layer3 is larger than the thickness t2 of the SUS304 of the high thermalexpansion layer 2, whereby the high-temperature bimetal 1 having thelarge bending coefficient K1 in the low temperature range of less thanthe Curie point (about 200° C.) can be easily obtained.

According to the first embodiment, as hereinabove described, thehigh-temperature bimetal 1 is formed such that the mass (oxidation massincrease) of the high-temperature bimetal 1 increased by the oxidationof the high-temperature bimetal 1 (the high thermal expansion layer 2and the low thermal expansion layer 3) resulting from the rise in thetemperature to the upper limit (about 700° C.) of the operatingtemperatures in the high temperature range of not less than the Curiepoint (about 200° C.) is not more than about 1.5 mg per cubiccentimeter. Thus, the thickness of the high-temperature bimetal 1increased by the oxidation can be rendered not more than about 1% of thetotal thickness t1 (=t2+t3) of the high-temperature bimetal 1 before theoxidation of the high-temperature bimetal 1. Thus, the property (bendingcoefficients K1 and K2 or the like) of the high-temperature bimetal 1can be inhibited from changing to such an extent that a practicalproblem is caused by an increase in the total thickness t1 of thehigh-temperature bimetal 1 by more than about 1% due to the oxidation.

According to the first embodiment, as hereinabove described, the thermalexpansion coefficient (about 15.8×10⁻⁶/K) of the 36Ni-6Nb—Fe alloy ofthe low thermal expansion layer 3 in the high temperature range of notless than the Curie point (about 200° C.) is about 91% of the thermalexpansion coefficient (about 17.3×10⁻⁶/K) of the SUS304 of the highthermal expansion layer 2. Thus, the high-temperature bimetal 1 can beinhibited from being deformed to the side closer to the high thermalexpansion layer 2 in the high temperature range, and the deformation dueto bending of the high-temperature bimetal 1 in the high temperaturerange can be inhibited from increase due to a significant differencebetween the thermal expansion coefficient of the high thermal expansionlayer 2 and the thermal expansion coefficient of the low thermalexpansion layer 3 in the high temperature range.

According to the first embodiment, as hereinabove described, the thermalexpansion coefficient (about 15.8×10⁻⁶/K) of the low thermal expansionlayer 3 in the high temperature range is about 3.9 times the thermalexpansion coefficient (about 4.1×10⁻⁶/K) of the low thermal expansionlayer 3 in the low temperature range of less than the Curie point (about200° C.), whereby the deformation due to bending of the high-temperaturebimetal 1 in the low temperature range of less than the Curie point(about 200° C.) can be further inhibited from decrease.

According to the first embodiment, as hereinabove described, the thermalexpansion coefficient (about 4.1×10⁻⁶/K) of the 36Ni-6Nb—Fe alloy of thelow thermal expansion layer 3 in the low temperature range is about 24%of the thermal expansion coefficient (about 17.3×10⁻⁶/K) of the SUS304of the high thermal expansion layer 2. Thus, the difference between thethermal expansion coefficient of the high thermal expansion layer 2 inthe low temperature range and the thermal expansion coefficient of thelow thermal expansion layer 3 in the low temperature range can berendered large, and hence the high-temperature bimetal 1 in the lowtemperature range can be more highly deformed by bending.

According to the first embodiment, as hereinabove described, the settemperature T2 at which the side of the high-temperature bimetal 1closer to the low thermal expansion layer 3 comes into contact with thestopper 5 provided on the employed prescribed device is close to theCurie point (about 200° C.) of the low thermal expansion layer 3 of thehigh-temperature bimetal 1 and higher than the Curie point. Thus, thelow thermal expansion layer 3 comes into contact with the stopper member5 in the high temperature range of not less than the Curie point inwhich accumulation of thermal stress in the high-temperature bimetal 1is inhibited, and hence thermal stress resulting from contact with thestopper member 5 can be hardly accumulated in the high-temperaturebimetal 1. Further, the low thermal expansion layer 3 comes into contactwith the stopper member 5 at a temperature close to the Curie point, andhence a state where the thermal stress resulting from contact with thestopper member 5 is hardly accumulated in the high-temperature bimetal 1is available over a wide temperature range.

Second Embodiment

A second embodiment of the present invention is now described withreference to FIG. 1. In relation to a high-temperature bimetal 101according to this second embodiment, a case where a low thermalexpansion layer 103 is made of a 40Ni-10Cr—Fe alloy dissimilarly to theaforementioned first embodiment is described.

In the high-temperature bimetal 101 according to the second embodimentof the present invention, the low thermal expansion layer 103 is made ofthe 40Ni-10Cr—Fe alloy containing about 40 mass % of Ni, about 10 mass %of Cr, Fe, and trace unavoidable impurities. Fe is a basic constituentof the 40Ni-10Cr—Fe alloy and occupies the balance other than Ni, Cr,and unavoidable impurities. The 40Ni-10Cr—Fe alloy of the low thermalexpansion layer 103 has a Curie point of about 200° C. Thus, the Curiepoint (about 200° C.) of a thermosensitive magnetic metal of the lowthermal expansion layer 103 is included in an operating temperaturerange of at least about −70° C. and not more than about 700° C. in whichthe high-temperature bimetal 101 can be employed. Further, in thehigh-temperature bimetal 101, an operating temperature range (about 500°C.) of a high temperature range of at least the Curie point (about 200°C.) and not more than about 700° C. is larger than an operatingtemperature range (about 270° C.) of a low temperature range of at leastabout −70° C. and less than about 200° C.

The 40Ni-10Cr—Fe alloy of the low thermal expansion layer 103 is'formedto have a thermal expansion coefficient of about 8.2×10⁻⁶/K in the lowtemperature range of less than the Curie point (about 200° C.) and athermal expansion coefficient of about 16.8×10⁻⁶/K in the hightemperature range of not less than the Curie point. The 40Ni-10Cr—Fealloy of the low thermal expansion layer 103 is formed such that thethermal expansion coefficient (about 8.2×10⁻⁶/K) thereof in the lowtemperature range of less than the Curie point is smaller than thethermal expansion coefficient (about 16.8×10⁻⁶/K) thereof in the hightemperature range of not less than the Curie point. The thermalexpansion coefficient (about 16.8×10⁻⁶/K) of the low thermal expansionlayer 103 in the high temperature range is about twice the thermalexpansion coefficient (about 8.2×10⁻⁶/K) of the low thermal expansionlayer 103 in the low temperature range.

Thus, a difference (about 0.5×10⁻⁶/K) between the thermal expansioncoefficient (about 17.3×10⁻⁶/K) of SUS304 of a high thermal expansionlayer 2 in the high temperature range and the thermal expansioncoefficient (about 16.8×10⁻⁶/K) of the low thermal expansion layer 103in the high temperature range is smaller than a difference (about9.1×10⁻⁶/K) between the thermal expansion coefficient (about17.3×10⁻⁶/K) of the SUS304 of the high thermal expansion layer 2 in thelow temperature range and the thermal expansion coefficient (about8.2×10⁻⁶/K) of the low thermal expansion layer 103 in the lowtemperature range.

The thermal expansion coefficients (about 8.2×10⁻⁶/K and about16.8×10⁻⁶/K) of the 40Ni-10Cr—Fe alloy of the low thermal expansionlayer 103 at less than the Curie point (about 200° C.) and not less thanthe Curie point are smaller than the thermal expansion coefficient(about 17.3×10⁻⁶/K) of the SUS304 of the high thermal expansion layer 2.Specifically, the thermal expansion coefficient (about 8.2×10⁻⁶/K) ofthe 40Ni-10Cr—Fe alloy of the low thermal expansion layer 103 in the lowtemperature range of less than the Curie point (about 200° C.) is about47% of the thermal expansion coefficient (about 17.3×10⁻⁶/K) of theSUS304 of the high thermal expansion layer 2. Further, the thermalexpansion coefficient (about 16.8×10⁻⁶/K) of the 40Ni-10Cr—Fe alloy ofthe low thermal expansion layer 103 in the high temperature range of notless than the Curie point is about 97% of the thermal expansioncoefficient (about 17.3×10⁻⁶/K) of the SUS304 of the high thermalexpansion layer 2. The thermal expansion coefficient of the low thermalexpansion layer 103 in the low temperature range is preferably not morethan about 50% of the thermal expansion coefficient of the high thermalexpansion layer 2, and the thermal expansion coefficient of the lowthermal expansion layer 103 in the high temperature range is preferablyat least about 70% and less than about 100% of the thermal expansioncoefficient of the high thermal expansion layer 2.

The high-temperature bimetal 101 has a bending coefficient K1 of about2.3×10⁻⁶/K in the low temperature range of less than the Curie point(about 200° C.) and a bending coefficient K2 of about 1.1×10⁻⁶/K in thehigh temperature range of not less than the Curie point. Thehigh-temperature bimetal 101 is formed such that the bending coefficientK2 (about 1.1×10⁻⁶/K) is smaller than the bending coefficient K1 (about2.3×10⁻⁶/K).

As shown in FIG. 1, the thickness t2 of the SUS304 of the high thermalexpansion layer 2 of the high-temperature bimetal 101 and the thicknesst3 of the 40Ni-10Cr—Fe alloy of the low thermal expansion layer 103 ofthe high-temperature bimetal 101 satisfy a relation: t2:t3=about45:about 55. In other words, the thickness t3 of the 40Ni-10Cr—Fe alloyof the low thermal expansion layer 103 is larger than the thickness t2of the SUS304 of the high thermal expansion layer 2. The structure anddeformation due to bending of the high-temperature bimetal according tothe second embodiment are similar to those of the high-temperaturebimetal according to the aforementioned first embodiment.

A method for manufacturing the high-temperature bimetal 101 according tothe second embodiment of the present invention is now described withreference to FIG. 1.

Plate-like SUS304 having a thickness of about 1.5 mm and a plate-like40Ni-10Cr—Fe alloy having a thickness of about 1.8 mm arecold-pressure-bonded to each other at a rolling reduction of about 60.6%thereby forming a bimetal made of a two-layered cladding material havinga thickness of about 1.3 mm. Then, diffusion annealing is performedunder a hydrogen atmosphere at about 1050° C. for about three minutes.Thus, the bond strength between a high thermal expansion layer and a lowthermal expansion layer of the bimetal can be improved. Thereafter, thebimetal having a thickness of about 1.3 mm is cold-rolled to have athickness t1 (see FIG. 1) of about 0.2 mm. Thus, the high-temperaturebimetal 101 (see FIG. 1) according to the second embodiment is formed.

Also in the aforementioned pressure-bonding and rolling, the ratiobetween the thickness of the plate-like SUS304 and the thickness of theplate-like 40Ni-10Cr—Fe alloy remains unchanged. Thus, the thickness t2(see FIG. 1) of the high thermal expansion layer 2 made of the SUS304and the thickness t3 (see FIG. 1) of the low thermal expansion layer 103made of the 40Ni-10Cr—Fe alloy satisfy a relation: t2:t3=about 1.5:about1.8=about 45:about 55. In other words, the proportion of the thicknesst3 of the 40Ni-10Cr—Fe alloy of the low thermal expansion layer 103 tothe thickness t1 of the high-temperature bimetal 101 is about 0.55,whereby the thickness t3 of the 40Ni-10Cr—Fe alloy of the low thermalexpansion layer 103 is larger than the thickness t2 of the SUS304 of thehigh thermal expansion layer 2.

According to the second embodiment, as hereinabove described, the lowthermal expansion layer 103 is made of the 40Ni-10Cr—Fe alloy containingabout 40 mass % of Ni, about 10 mass % of Cr, Fe, and trace unavoidableimpurities, whereby the high-temperature bimetal 101 including thethermosensitive magnetic metal having a Curie point of about 200° C. canbe obtained. Further, the high-temperature bimetal 101 beingoxidation-resistant enough not to cause a problem even if thetemperature rises to the upper limit (about 700° C.) of operatingtemperatures of the high-temperature bimetal 101 and including thethermosensitive magnetic metal capable of inhibiting an excessiveincrease in a thermal expansion coefficient can be obtained.

According to the second embodiment, as hereinabove described, thethermal expansion coefficient (about 16.8×10⁻⁶/K) of the 40Ni-10Cr—Fealloy of the low thermal expansion layer 103 in the high temperaturerange of not less than the Curie point (about 200° C.) is about 97% ofthe thermal expansion coefficient (about 17.3×10⁻⁶/K) of the SUS304 ofthe high thermal expansion layer 2. Thus, the high-temperature bimetal101 can be inhibited from being deformed to the side closer to the highthermal expansion layer 2 in the high temperature range, and thedeformation due to bending of the high-temperature bimetal 101 in thehigh temperature range can be inhibited from increase due to asignificant difference between the thermal expansion coefficient of thehigh thermal expansion layer 2 and the thermal expansion coefficient ofthe low thermal expansion layer 103 in the high temperature range.

According to the second embodiment, as hereinabove described, thethermal expansion coefficient (about 16.8×10⁻⁶/K) of the low thermalexpansion layer 103 in the high temperature range is about twice thethermal expansion coefficient (about 8.2×10⁻⁶/K) of the low thermalexpansion layer 103 in the low temperature range of less than the Curiepoint (about 200° C.), whereby the deformation due to bending of thehigh-temperature bimetal 101 in the low temperature range of less thanthe Curie point (about 200° C.) can be further inhibited from decrease.

According to the second embodiment, as hereinabove described, thethermal expansion coefficient (about 8.2×10⁻⁶/K) of the low thermalexpansion layer 103 in the low temperature range is about 47% of thethermal expansion coefficient (about 17.3×10⁻⁶/K) of the high thermalexpansion layer 2. Thus, the difference between the thermal expansioncoefficient of the high thermal expansion layer 2 in the low temperaturerange and the thermal expansion coefficient of the low thermal expansionlayer 103 in the low temperature range can be rendered large, and hencethe high-temperature bimetal 101 in the low temperature range can bemore highly deformed by bending. The remaining effects of thehigh-temperature bimetal according to the second embodiment are similarto those of the high-temperature bimetal according to the aforementionedfirst embodiment.

Third Embodiment

A third embodiment of the present invention is now described withreference to FIG. 1. In relation to a high-temperature bimetal 201according to this third embodiment, a case where a high thermalexpansion layer 202 is made of a 12Cr-18Ni—Fe alloy while a low thermalexpansion layer 203 is made of a 36Ni-2Nb—Fe alloy dissimilarly to theaforementioned first embodiment is described.

In the high-temperature bimetal 201 according to the third embodiment ofthe present invention, the high thermal expansion layer 202 is made of a12Cr-18Ni—Fe alloy containing about 12 mass % of Cr, about 18 mass % ofNi, Fe, and trace unavoidable impurities. Fe is a basic constituent ofthe 12Cr-18Ni—Fe alloy and occupies the balance other than Ni, Cr, andunavoidable impurities. The 12Cr-18Ni—Fe alloy of the high thermalexpansion layer 202 is austenitic stainless steel and has a thermalexpansion coefficient of about 19.0×10⁻⁶/K.

According to the third embodiment, the low thermal expansion layer 203is made of the 36Ni-2Nb—Fe alloy containing about 36 mass % of Ni, about2 mass % of Nb, Fe, and trace unavoidable impurities. Fe is a basicconstituent of the 36Ni-2Nb—Fe alloy and occupies the balance other thanNi, Nb, and unavoidable impurities. The 36Ni-2Nb—Fe alloy of the lowthermal expansion layer 203 has a Curie point of about 170° C. Thus, theCurie point (about 170° C.) of a thermosensitive magnetic metal of thelow thermal expansion layer 203 is included in an operating temperaturerange of at least about −70° C. and not more than about 700° C. in whichthe high-temperature bimetal 201 can be employed. Further, in thehigh-temperature bimetal 201, an operating temperature range (about 530°C.) of a high temperature range of at least the Curie point (about 170°C.) and not more than about 700° C. is larger than an operatingtemperature range (about 200° C.) of a low temperature range of at leastabout −70° C. and less than about 170° C.

The 36Ni-2Nb—Fe alloy of the low thermal expansion layer 203 is formedto have a thermal expansion coefficient of about 3.0×10⁻⁶/K in the lowtemperature range of less than the Curie point (about 170° C.) and athermal expansion coefficient of about 15.7×10⁻⁶/K in the hightemperature range of not less than the Curie point. The 36Ni-2Nb—Fealloy of the low thermal expansion layer 203 is formed such that thethermal expansion coefficient (about 3.0×10⁻⁶/K) thereof in the lowtemperature range of less than the Curie point is smaller than thethermal expansion coefficient (about 15.7×10⁻⁶/K) thereof in the hightemperature range of not less than the Curie point. The thermalexpansion coefficient (about 15.7×10⁻⁶/K) of the low thermal expansionlayer 203 in the high temperature range is about 5.2 times the thermalexpansion coefficient (about 3.0×10⁻⁶/K) of the low thermal expansionlayer 203 in the low temperature range.

Thus, a difference (about 3.3×10⁻⁶/K) between the thermal expansioncoefficient (about 19.0×10⁻⁶/K) of the high thermal expansion layer 202in the high temperature range and the thermal expansion coefficient(about 15.7×10⁻⁶/K) of the low thermal expansion layer 203 in the hightemperature range is smaller than a difference (about 16.0×10⁻⁶/K)between the thermal expansion coefficient (about 19.0×10⁻⁶/K) of thehigh thermal expansion layer 202 in the low temperature range and thethermal expansion coefficient (about 3.0×10⁻⁶/K) of the low thermalexpansion layer 203 in the low temperature range.

The thermal expansion coefficients (about 3.0×10⁻⁶/K and about15.7×10⁻⁶/K) of the 36Ni-2Nb—Fe alloy of the low thermal expansion layer203 at less than the Curie point (about 170° C.) and not less than theCurie point are smaller than the thermal expansion coefficient (about19.0×10⁻⁶/K) of the 12Cr-18Ni—Fe alloy of the high thermal expansionlayer 202. Specifically, the thermal expansion coefficient (about3.0×10⁻⁶/K) of the 36Ni-2Nb—Fe alloy of the low thermal expansion layer203 in the low temperature range of less than the Curie point (about170° C.) is about 16% of the thermal expansion coefficient (about19.0×10⁻⁶/K) of the 12Cr-18Ni—Fe alloy of the high thermal expansionlayer 202. Further, the thermal expansion coefficient (about15.7×10⁻⁶/K) of the 36Ni-2Nb—Fe alloy of the low thermal expansion layer203 in the high temperature range of not less than the Curie point isabout 83% of the thermal expansion coefficient (about 19.0×10⁻⁶/K) ofthe 12Cr-18Ni—Fe alloy of the high thermal expansion layer 202.

The high-temperature bimetal 201 has a bending coefficient K1 of about11.9×10⁻⁶/K in the low temperature range of less than the Curie point(about 170° C.) and a bending coefficient K2 of about 6.5×10⁻⁶/K in thehigh temperature range of not less than the Curie point. Thehigh-temperature bimetal 201 is formed such that the bending coefficientK2 (about 6.5×10⁻⁶/K) is smaller than the bending coefficient K1 (about11.9×10⁻⁶/K). The structure and deformation due to bending of thehigh-temperature bimetal according to the third embodiment are similarto those of the high-temperature bimetal according to the aforementionedfirst embodiment, and a method for manufacturing the high-temperaturebimetal according to the third embodiment is similar to the method formanufacturing the high-temperature bimetal according to theaforementioned first embodiment.

According to the third embodiment, as hereinabove described, the lowthermal expansion layer 203 is made of the 36Ni-2Nb—Fe alloy containingabout 36 mass % of Ni, about 2 mass % of Nb, Fe, and trace unavoidableimpurities, whereby the high-temperature bimetal 201 including thethermosensitive magnetic metal having a Curie point of about 170° C. canbe obtained. Further, the high-temperature bimetal 201 beingoxidation-resistant enough not to cause a problem even if thetemperature rises to the upper limit (about 700° C.) of operatingtemperatures of the high-temperature bimetal 201 and including thethermosensitive magnetic metal capable of inhibiting a reduction inworkability can be obtained.

According to the third embodiment, as hereinabove described, the thermalexpansion coefficient (about 15.7×10⁻⁶/K) of the 36Ni-2Nb—Fe alloy ofthe low thermal expansion layer 203 in the high temperature range of notless than the Curie point (about 170° C.) is about 83% of the thermalexpansion coefficient (about 19.0×10⁻⁶/K) of the 12Cr-18Ni—Fe alloy ofthe high thermal expansion layer 202. Thus, the high-temperature bimetal201 can be inhibited from being deformed to the side closer to the highthermal expansion layer 202 in the high temperature range, and thedeformation due to bending of the high-temperature bimetal 201 in thehigh temperature range can be inhibited from increase due to asignificant difference between the thermal expansion coefficient of thehigh thermal expansion layer 202 and the thermal expansion coefficientof the low thermal expansion layer 203 in the high temperature range.

According to the third embodiment, as hereinabove described, the thermalexpansion coefficient (about 15.7×10⁻⁶/K) of the low thermal expansionlayer 203 in the high temperature range is about 5.2 times the thermalexpansion coefficient (about 3.0×10⁻⁶/K) of the low thermal expansionlayer 203 in the low temperature range of less than the Curie point(about 170° C.), whereby the deformation due to bending of thehigh-temperature bimetal 201 in the low temperature range of less thanthe Curie point (about 170° C.) can be further inhibited from decrease.

According to the third embodiment, as hereinabove described, the thermalexpansion coefficient (about 3.0×10⁻⁶/K) of the low thermal expansionlayer 203 in the low temperature range is about 16% of the thermalexpansion coefficient (about 19.0×10⁻⁶/K) of the high thermal expansionlayer 202. Thus, the difference between the thermal expansioncoefficient of the high thermal expansion layer 202 in the lowtemperature range and the thermal expansion coefficient of the lowthermal expansion layer 203 in the low temperature range can be renderedlarge, and hence the high-temperature bimetal 201 in the low temperaturerange can be more highly deformed by bending. The remaining effects ofthe high-temperature bimetal according to the third embodiment aresimilar to those of the high-temperature bimetal according to theaforementioned first embodiment.

EXAMPLE

Measurement of a displacement and measurement of an oxidation massincrease conducted in order to confirm the effects of thehigh-temperature bimetals 1, 101, and 201 according to theaforementioned first to third embodiments are now described withreference to FIGS. 1 and 5 to 10.

In the measurement of a displacement and the measurement of an oxidationmass increase hereinafter described, a high-temperature bimetal preparedby the method for manufacturing the high-temperature bimetal 1 accordingto the aforementioned first embodiment was employed as an Example 1corresponding to the high-temperature bimetal 1 (see FIG. 1) accordingto the aforementioned first embodiment. Specifically, thehigh-temperature bimetal (SUS304/36Ni-6Nb—Fe alloy) constituted by ahigh terminal expansion layer made of SUS304 and a low thermal expansionlayer made of a 36Ni-6Nb—Fe alloy was employed as the Example 1. Thethickness t1 (see FIG. 5) of the high-temperature bimetal according tothe Example 1 is 0.2 mm, and the thickness t2 (see FIG. 5) of the SUS304of the high thermal expansion layer and the thickness t3 (see FIG. 5) ofthe 36Ni-6Nb—Fe alloy of the low thermal expansion layer satisfy arelation: t2:t3=47:53 (=0.094 mm:0.106 mm).

A high-temperature bimetal prepared by the method for manufacturing thehigh-temperature bimetal 101 according to the aforementioned secondembodiment was employed as an Example 2 corresponding to thehigh-temperature bimetal 101 (see FIG. 1) according to theaforementioned second embodiment. Specifically, the high-temperaturebimetal (SUS304/40Ni-10Cr—Fe alloy) constituted by a high terminalexpansion layer made of SUS304 and a low thermal expansion layer made ofa 40Ni-10Cr—Fe alloy was employed as the Example 2. The thickness t1(see FIG. 5) of the high-temperature bimetal according to the Example 2is 0.2 mm, and the thickness t2 (see FIG. 5) of the SUS304 of the highthermal expansion layer and the thickness t3 (see FIG. 5) of the40Ni-10Cr—Fe alloy of the low thermal expansion layer satisfy arelation: t2:t3=45:55 (=0.09 mm:0.11 mm).

A high-temperature bimetal prepared by the method (similar to the methodfor manufacturing the high-temperature bimetal 1 according to the firstembodiment) for manufacturing the high-temperature bimetal 201 accordingto the aforementioned third embodiment was employed as an Example 3corresponding to the high-temperature bimetal 201 (see FIG. 1) accordingto the aforementioned third embodiment. Specifically, thehigh-temperature bimetal (12Cr-18Ni—Fe alloy/36Ni-2Nb—Fe alloy)constituted by a high terminal expansion layer made of a 12Cr-18Ni—Fealloy and a low thermal expansion layer made of a 36Ni-2Nb—Fe alloy wasemployed as the Example 3.

(Measurement of Displacement)

The measurement of a displacement is first described. In thismeasurement of a displacement, a high-temperature bimetal 301 having athickness t1 of 0.2 mm, a length L of 15 mm, and a width of 2 mm (notshown) was employed to perform the measurement, as shown in FIG. 5. Thehigh-temperature bimetal 301 was formed not to be deformed by bending inan initial state (ordinary temperature T1 (25° C.)).

In the measurement of a displacement, a first end of thehigh-temperature bimetal 301 in a length direction was fixed with afixing portion 304. Then, the temperature rises to maximum of 700° C.from the initial state, whereby the high-temperature bimetal 301 wasdeformed by bending to the side closer to a low thermal expansion layer303, as shown in FIG. 6. At this time, the displacement D (mm) of thehigh-temperature bimetal 301 resulting from deformation due to bendingwith changes in temperature T (° C.) was measured. Further, the bendingcoefficient K of the high-temperature bimetal 301 was calculated on thebasis of the measured displacement D and the following expression (1):

K=(t1)ΔD/L ² ΔT   (1)

Here, t1 represents the thickness (see FIG. 5) of the high-temperaturebimetal 301 and is equal to 0.2 mm. L represents the width (see FIG. 5)of the high-temperature bimetal 301 and is equal to 15 mm. ΔD representsa difference between a first displacement at an arbitrary firsttemperature and a second displacement at an arbitrary second temperaturedifferent from the first temperature. ΔT represents a difference betweenthe first temperature and the second temperature.

In the measurement of a displacement, each of the aforementioned Example1 (SUS304/36Ni-6Nb—Fe alloy), Example 2 (SUS304/40Ni-10Cr—Fe alloy), andExample 3 (12Cr-18Ni—Fe alloy/36Ni-2Nb—Fe alloy) was employed as thehigh-temperature bimetal 301. On the other hand, the high-temperaturebimetal 301 (SUS304/18Cr—Fe alloy) having a high thermal expansion layer302 made of SUS304 and the low thermal expansion layer 303 made of a18Cr—Fe alloy containing 18 mass % of Cr, Fe, and trace unavoidableimpurities was employed as a comparative example 1 to be compared withthe Example 1. The 18Cr—Fe alloy of the low thermal expansion layer 303of the high-temperature bimetal 301 according to this comparativeexample 1 has no Curie point. The thickness t1 of the high-temperaturebimetal 301 according to the comparative example 1 is 0.2 mm, and thethickness t2 (see FIG. 5) of the SUS304 of the high thermal expansionlayer 302 of the high-temperature bimetal 301 according to thecomparative example 1 and the thickness t3 (see FIG. 5) of the 18Cr—Fealloy of the low thermal expansion layer 303 of the high-temperaturebimetal 301 according to the comparative example 1 satisfy a relation:t2:t3=50:50 (=0.1 mm:0.1 mm). A high-temperature bimetal having abending coefficient K equal to a bending coefficient K1 in a lowtemperature range of less than a Curie point according to the Example 2and having no Curie point (having the bending coefficient K remainingunchanged) was assumed as a comparative example 2 to be compared withthe Example 2. Similarly, a high-temperature bimetal having a bendingcoefficient K equal to a bending coefficient K1 in a low temperaturerange of less than a Curie point according to the Example 3 and havingno Curie point (having the bending coefficient K remaining unchanged)was assumed as a comparative example 3 to be compared with the Example3.

When a bending coefficient K was calculated, the bending coefficient Kwas separated into a bending coefficient K1 in a low temperature rangeof less than a Curie point and a bending coefficient K2 in a hightemperature range of not less than the Curie point and calculated in acase of a sample having a Curie point according to each of the Examples1 to 3. Specifically, the bending coefficient K1 in the low temperaturerange of less than the Curie point was calculated on the basis of adisplacement D1 (=0) at the ordinary temperature T1 (25° C.) and adisplacement D2 at 100° C. In other words, ΔT=75 (=100−25), ΔD=D2−D1(=D2), t1=0.2 mm, and L=15 mm were substituted in the above expression(1), whereby the bending coefficient K1 in the low temperature range ofless than the Curie point was calculated. The bending coefficient K2 inthe high temperature range of not less than the Curie point wascalculated on the basis of a displacement D3 at 250° C. and adisplacement D4 at 300° C. In other words, ΔT=50 (=300−250), ΔD=D4-D3,t1=0.2 mm, and L=15 mm were substituted in the above expression (1),whereby the bending coefficient K2 in the high temperature range of notless than the Curie point was calculated.

When the bending coefficient K was calculated, the bending coefficient Kwas calculated on the basis of the displacement D1 (=0) at the ordinarytemperature T1 (25° C.) and the displacement D2 at 100° C. in a case ofa sample having no Curie point according to the comparative example 1.In other words, ΔT=75 (=100−25), ΔD=D2−D1 (=D2), t1=0.2 mm, and L=15 mmwere substituted in the above expression (1), whereby the bendingcoefficient K was calculated.

Experimental results of measurement of a displacement shown in FIGS. 7to 10 showed that as for the Example 1, the high-temperature bimetal 301according to the Example 1 was deformed by bending substantiallysimilarly to the high-temperature bimetal 301 according to thecomparative example 1 in the low temperature range of less than theCurie point (200° C.) shown in FIG. 7, as shown in FIG. 8. On the otherhand, in the high temperature range of not less than the Curie point,the displacement D of deformation due to bending of the high-temperaturebimetal 301 according to the Example 1 was small compared with that ofthe high-temperature bimetal 301 according to the comparative example 1.In other words, it has been confirmed that in the high temperature rangeof not less than the Curie point, the slope (displacement per unittemperature) of a graph of the displacement D of the high-temperaturebimetal 301 according to the Example 1 is smaller than the slope(displacement per unit temperature) of a graph of the displacement D ofthe high-temperature bimetal 301 according to the comparative example 1.

Thus, it is presumed that at 700° C., which is an upper limit of anoperating temperature range of the high-temperature bimetal 301according to the Example 1, a difference (displacement of the Example 1in the high temperature range) D5 between the displacement D ofdeformation due to bending of the high-temperature bimetal 301 accordingto the Example 1 at 700° C. and the displacement D of deformation due tobending of the high-temperature bimetal 301 according to the Example 1at 200° C., which is the Curie point, is about one-third as comparedwith a difference (displacement of the comparative example 1 in the hightemperature range) D6 between the displacement D of deformation due tobending of the high-temperature bimetal 301 according to the comparativeexample 1 at 700° C. and the displacement D of deformation due tobending of the high-temperature bimetal 301 according to the comparativeexample 1 at 200° C. Thus, it is presumed that in the high temperaturerange of not less than the Curie point, the high-temperature bimetal 301according to the Example 1 can further inhibit an increase in thermalstress as compared with the high-temperature bimetal 301 according tothe comparative example 1.

As for the Example 2, the high-temperature bimetal 301 according to theExample 2 was deformed by bending similarly to the assumedhigh-temperature bimetal according to the comparative example 2 in thelow temperature range of less than the Curie point (200° C.) shown inFIG. 7, as shown in FIG. 8. On the other hand, in the high temperaturerange of not less than the Curie point, the displacement D ofdeformation due to bending of the high-temperature bimetal 301 accordingto the Example 2 was small compared with that of the assumedhigh-temperature bimetal according to the comparative example 2. Inother words, it has been confirmed that in the high temperature range ofnot less than the Curie point, the slope (displacement per unittemperature) of a graph of the displacement D of the high-temperaturebimetal 301 according to the Example 2 is smaller than the slope(displacement per unit temperature) of a graph of the displacement D ofthe assumed high-temperature bimetal according to the comparativeexample 2.

Thus, it is presumed that at 700° C., which is an upper limit of anoperating temperature range of the high-temperature bimetal 301according to the Example 2, a difference (displacement of the Example 2in the high temperature range) D7 between the displacement D ofdeformation due to bending of the high-temperature bimetal 301 accordingto the Example 2 at 700° C. and the displacement D of deformation due tobending of the high-temperature bimetal 301 according to the Example 2at 200° C., which is the Curie point, is about one-sixth as comparedwith a difference (displacement of the comparative example 2 in the hightemperature range) D8 between the displacement D of deformation due tobending of the assumed high-temperature bimetal according to thecomparative example 2 at 700° C. and the displacement D of deformationdue to bending of the assumed high-temperature bimetal according to thecomparative example 2 at 200° C. Thus, it is presumed that in the hightemperature range of not less than the Curie point, the high-temperaturebimetal 301 according to the Example 2 can further inhibit an increasein thermal stress as compared with the assumed high-temperature bimetalaccording to the comparative example 2.

As for the Example 3, the high-temperature bimetal 301 according to theExample 3 was deformed by bending similarly to the assumedhigh-temperature bimetal according to the comparative example 3 in thelow temperature range of less than the Curie point (170° C.) shown inFIG. 7, as shown in FIG. 8. On the other hand, in the high temperaturerange of not less than the Curie point, the displacement D ofdeformation due to bending of the high-temperature bimetal 301 accordingto the Example 3 was small compared with that of the assumedhigh-temperature bimetal according to the comparative example 3. Inother words, it has been confirmed that in the high temperature range ofnot less than the Curie point, the slope (displacement per unittemperature) of a graph of the displacement D of the high-temperaturebimetal 301 according to the Example 3 is smaller than the slope(displacement per unit temperature) of a graph of the displacement D ofthe assumed high-temperature bimetal according to the comparativeexample 3. Thus, it is presumed that in the high temperature range ofnot less than the Curie point, the high-temperature bimetal 301according to the Example 3 can further inhibit an increase in thermalstress as compared with the assumed high-temperature bimetal accordingto the comparative example 3.

Data of displacements D at prescribed temperatures T (100° C., 250° C.,and 300° C.) shown in FIG. 9 was employed to calculate bendingcoefficients K shown in FIG. 10. Thus, it has been confirmable that inthe high-temperature bimetal 301 according to the Example 1, the bendingcoefficient K2 (3.3×10⁻⁶/K) in the high temperature range of not lessthan the Curie point (200° C.) is smaller than the bending coefficientK1 (6.7×10⁻⁶/K) in the low temperature range of less than the Curiepoint. It has been confirmable that in the high-temperature bimetal 301according to the Example 2, the bending coefficient K2 (1.1×10⁻⁶/K) inthe high temperature range of not less than the Curie point (200° C.) issmaller than the bending coefficient K1 (2.3×10⁻⁶/K) in the lowtemperature range of less than the Curie point. It has been confirmablethat in the high-temperature bimetal 301 according to the Example 3, thebending coefficient K2 (6.5×10⁻⁶/K) in the high temperature range of notless than the Curie point (170° C.) is smaller than the bendingcoefficient K1 (11.9×10⁻⁶/K) in the low temperature range of less thanthe Curie point.

(Measurement of Oxidation Mass Increase)

Secondly, measurement of an oxidation mass increase is described. Inthis measurement of an oxidation mass increase, a high-temperaturebimetal having a thickness of 0.2 mm, a width of 1.0 cm, and a length of3.0 cm, constituted by a high thermal expansion layer and a low thermalexpansion layer was employed to perform the measurement. In themeasurement of an oxidation mass increase, the masses of samples afterheat treatment by holding the samples for 15 hours at 500° C., 600° C.,and 700° C. (highest acceptable temperature) were measured. An oxidationmass increase was calculated with the following expression (2):

oxidation mass increase=(mass after heat treatment−mass before heattreatment)/(1.0 cm×3.0 cm)   (2)

In the measurement of an oxidation mass increase, the Example 1(SUS304/36Ni-6Nb—Fe alloy), the Example 2 (SUS304/40Ni-10Cr—Fe alloy),and the Example 3 (12Cr-18Ni—Fe alloy/36Ni-2Nb—Fe alloy) employed in theaforementioned measurement of a displacement and the comparative example1 (SUS304/18Cr—Fe alloy) employed to be compared with the Example 1 inthe aforementioned measurement of a displacement each were employed as ahigh-temperature bimetal. On the other hand, a bimetal having a highthermal expansion layer made of a 23Ni-5Mn—Fe alloy containing 23 mass %of Ni, 5 mass % of Mn, Fe, and trace unavoidable impurities and a lowthermal expansion layer made of a 36Ni—Fe alloy containing 36 mass % ofNi, Fe, and trace unavoidable impurities was employed as a comparativeexample 4. A bimetal having a high thermal expansion layer made of a20Ni-6Cr—Fe alloy containing 20 mass % of Ni, 6 mass % of Cr, Fe, andtrace unavoidable impurities and a low thermal expansion layer made of a36Ni—Fe alloy was employed as a comparative example 5. A bimetal havinga high thermal expansion layer made of a 20Ni-6Cr—Fe alloy and a lowthermal expansion layer made of a 42Ni—Fe alloy containing 42 mass % ofNi, Fe, and trace unavoidable impurities was employed as a comparativeexample 6.

If an oxidation mass increase is more than 1.5 mg (acceptable value) percubic centimeter, an increase in the thickness of a high-temperaturebimetal due to oxidation is more than 2 μm and exceeds 1% of the totalthickness (0.2 mm) of the high-temperature bimetal before the oxidation.Thus, if the oxidation mass increase is more than 1.5 mg per cubiccentimeter, the property (bending coefficient K or the like) of thehigh-temperature bimetal changes to such an extent that a practicalproblem is caused.

Experimental results of measurement of an oxidation mass increase shownin FIG. 11 showed that the oxidation mass increases of thehigh-temperature bimetals according to the Examples 1, 2, and 3 and thecomparative example 1 and the bimetals according to the comparativeexamples 4 to 6 were not more than 1.5 mg per cubic centimeter when thehigh-temperature bimetals and the bimetals were heat-treated at 500° C.and 600° C. However, when the high-temperature bimetals and the bimetalswere heat-treated at 700° C. (highest acceptable temperature), theoxidation mass increases of the high-temperature bimetals according tothe Examples 1, 2, and 3 and the comparative example 1 were not morethan 1.5 mg (Example 1: 1.03 mg, Example 2: 0.26 mg, Example 3: 1.38 mg,comparative example 1: 0.07 mg) per cubic centimeter whereas thebimetals according to the comparative examples 4 to 6 were more than 1.5mg (comparative example 4: 2.83 mg, comparative example 5: 2.01 mg,comparative example 6: 2.09 mg) per cubic centimeter. Thus, it ispresumed that the properties (bending coefficients K or the like) of thehigh-temperature bimetals according to the Examples 1, 2, and 3 and thecomparative example 1 do not change to such an extent that a practicalproblem is caused whereas the properties of the bimetals according tothe comparative examples 4 to 6 change to such an extent that apractical problem is caused, if the temperature rises to the highestacceptable temperature (700° C.)

It is presumed that the oxidation mass increase of the high-temperaturebimetal according to the Example 1 was not more than 1.5 mg per cubiccentimeter because the high thermal expansion layer made of the SUS304contained Cr and the low thermal expansion layer made of the 36Ni-6Nb—Fealloy contained Nb thereby improving the oxidation resistance of each ofthe high thermal expansion layer and the low thermal expansion layer. Itis presumed that the oxidation mass increase of the high-temperaturebimetal according to the Example 2 was not more than 1.5 mg per cubiccentimeter because the high thermal expansion layer made of the SUS304and the low thermal expansion layer made of the 40Ni-10Cr—Fe alloy eachcontained Cr thereby improving the oxidation resistance of each of thehigh thermal expansion layer and the low thermal expansion layer. It ispresumed that the oxidation mass increase of the high-temperaturebimetal according to the Example 3 was not more than 1.5 mg per cubiccentimeter because the high thermal expansion layer made of the12Cr-18Ni—Fe alloy contained Cr and the low thermal expansion layer madeof the 36Ni-2Nb—Fe alloy contained Nb thereby improving the oxidationresistance of each of the high thermal expansion layer and the lowthermal expansion layer.

It is presumed that the oxidation mass increase of the high-temperaturebimetal according to the comparative example 1 was not more than 1.5 mg(0.07 mg) per cubic centimeter because the high thermal expansion layermade of the SUS304 and the low thermal expansion layer made of the18Cr—Fe alloy each contained Cr thereby improving the oxidationresistance of each of the high thermal expansion layer and the lowthermal expansion layer.

It is presumed from the aforementioned results of measurement of adisplacement and measurement of an oxidation mass increase that in thehigh temperature range of not less than the Curie point (200° C.), thehigh-temperature bimetal according to the Example 1 constituted by thehigh thermal expansion layer made of SUS304 and the low thermalexpansion layer made of the 36Ni-6Nb—Fe alloy can further inhibit anincrease in thermal stress as compared with the high-temperature bimetalaccording to the comparative example 1 having no Curie point while theproperty (bending coefficient K or the like) of the high-temperaturebimetal does not change to such an extent that a practical problem iscaused even if the temperature rises to the highest acceptabletemperature (700° C.). Thus; it has been confirmable that accumulationof thermal stress in the high-temperature bimetal according to theExample 1 can be inhibited in the high temperature range of not lessthan the Curie point (200° C.) while the property of thehigh-temperature bimetal can be inhibited from changing to such anextent that a practical problem is caused.

It is presumed that in the high temperature range of not less than theCurie point (200° C.), the high-temperature bimetal according to theExample 2 constituted by the high thermal expansion layer made of SUS304and the low thermal expansion layer made of the 40Ni-10Cr—Fe alloy canfurther inhibit an increase in thermal stress as compared with theassumed high-temperature bimetal according to the comparative example 2having no Curie point while the property (bending coefficient K or thelike) of the high-temperature bimetal do not change to such an extentthat a practical problem is caused even if the temperature rises to thehighest acceptable temperature (700° C.). Thus, it has been confirmablethat accumulation of thermal stress in the high-temperature bimetalaccording to the Example 2 can be inhibited in the high temperaturerange of not less than the Curie point (200° C.) while the property ofthe high-temperature bimetal can be inhibited from changing to such anextent that a practical problem is caused.

It is presumed that in the high temperature range of not less than theCurie point (170° C.), the high-temperature bimetal according to theExample 3 constituted by the high thermal expansion layer made of the12Cr-18Ni—Fe alloy and the low thermal expansion layer made of the36Ni-2Nb—Fe alloy can further inhibit an increase in thermal stress ascompared with the assumed high-temperature bimetal according to thecomparative example 3 having no Curie point while the property (bendingcoefficient K or the like) of the high-temperature bimetal do not changeto such an extent that a practical problem is caused even if thetemperature rises to the highest acceptable temperature (700° C.). Thus,it has been confirmable that accumulation of thermal stress in thehigh-temperature bimetal according to the Example 3 can be inhibited inthe high temperature range of not less than the Curie point (170° CYwhile the property of the high-temperature bimetal can be inhibited fromchanging to such an extent that a practical problem is caused.

The embodiments and Examples disclosed this time must be considered asillustrative in all points and not restrictive. The range of the presentinvention is shown not by the above description of the embodiments andExamples but by the scope of claims for patent, and all modificationswithin the meaning and range equivalent to the scope of claims forpatent are included.

For example, while the example of making the high thermal expansionlayer 2 of the SUS304 (18Cr-8Ni—Fe alloy) has been shown in each of theaforementioned first and second embodiments and the example of makingthe high thermal expansion layer 202 of the 12Cr-18Ni—Fe alloy has beenshown in the aforementioned third embodiment, the present invention isnot restricted to this, but the high thermal expansion layer may beSUS305 ((17 to 19)Cr-(8 to 10.5)Ni—Fe alloy), for example, as long asthe same is austenitic stainless steel.

While the example of making the low thermal expansion layer 3 of the36Ni-6Nb—Fe alloy has been shown in the aforementioned first embodiment,the example of making the low thermal expansion layer 103 of the40Ni-10Cr—Fe alloy has been shown in the aforementioned secondembodiment, and the example of making the low thermal expansion layer203 of the 36Ni-2Nb—Fe alloy has been shown in the aforementioned thirdembodiment, the present invention is not restricted to this, but thereis no particular limitation on the low thermal expansion layer as longas the same is a thermosensitive magnetic metal. The thermosensitivemagnetic metal of the low thermal expansion layer can have a Curie pointof at least about 100° C. by containing at least about 32 mass % of Ni.Further, the thermosensitive magnetic metal of the low thermal expansionlayer can have a Curie point of not more than about 400° C. bycontaining not more than about 45 mass % of Ni. Therefore, thethermosensitive magnetic metal of the low thermal expansion layer ispreferably a Ni—Fe alloy containing at least about 32 mass % and not,more than about 45 mass % of Ni.

While the example of making the low thermal expansion layer 3 of the36Ni-6Nb—Fe alloy has been shown in the aforementioned first embodiment,the example of making the low thermal expansion layer 103 of the40Ni-10Cr—Fe alloy has been shown in the aforementioned secondembodiment, and the example of making the low thermal expansion layer203 of the 36Ni-2Nb—Fe alloy has been shown in the aforementioned thirdembodiment, the present invention is not restricted to this, but thethermosensitive magnetic metal of the low thermal expansion layer may bea Ni—Fe alloy containing at least about 32 mass % and not more thanabout 45 mass % of Ni to which at least one of Nb, Cr, Al, Si, and Ti isadded. At this time, Al is preferably added in the range of at leastabout 1 mass % to not more than about 5 mass % if Al is added to theNi—Fe alloy. The reason is as follows. At least about 1 mass % of Al isadded to the Ni—Fe alloy, whereby the oxidation resistance of thethermosensitive magnetic metal can be improved. Further, not more thanabout 5 mass % of Al is added to the Ni—Fe alloy, whereby a reduction inthe workability of the thermosensitive magnetic metal due to anexcessive increase in the strength of the thermosensitive magnetic metalcan be inhibited.

In the thermosensitive magnetic metal of the low thermal expansionlayer, Si is preferably added in the range of at least about 1 mass % tonot more than about 5 mass % if Si is added to the Ni—Fe alloy. Thereason is as follows. At least about 1 mass % of Si is added to theNi—Fe alloy, whereby the oxidation resistance of the thermosensitivemagnetic metal can be improved. Further, not more than about 5 mass % ofSi is added to the Ni—Fe alloy, whereby a reduction in the workabilityof the thermosensitive magnetic metal due to an excessive increase inthe strength of the thermosensitive magnetic metal can be inhibited.

In the thermosensitive magnetic metal of the low thermal expansionlayer, Ti is preferably added in the range of at least about 0.2 mass %to not more than about 1 mass % if Ti is added to the Ni—Fe alloy. Thereason is as follows. At least about 0.2 mass % of Ti is added to theNi—Fe alloy, whereby the oxidation resistance of the thermosensitivemagnetic metal can be improved. Further, not-more than about 1 mass % ofTi is added to the Ni—Fe alloy, whereby a reduction in the workabilityof the thermosensitive'magnetic metal due to an excessive increase inthe strength of the thermosensitive magnetic metal can be inhibited.

While the example of making the low thermal expansion layer 3 of the36Ni-6Nb—Fe alloy has been shown in the aforementioned first embodimentand the example of making the low thermal expansion layer 203 of the36Ni-2Nb—Fe alloy has been shown in the aforementioned third embodiment,the present invention is not restricted to this, but the thermosensitivemagnetic metal of the low thermal expansion layer may be a Ni—Fe alloycontaining at least about 32 mass % and not more than about 45 mass % ofNi to which Nb is added in the range of at least about 2 mass % to notmore than about 8 mass %.

While the example of making the low thermal expansion layer 103 of the40Ni-10Cr—Fe alloy has been shown in the aforementioned secondembodiment, the present invention is not restricted to this, but thethermosensitive magnetic metal of the low thermal expansion layer may bea Ni—Fe alloy containing at least about 32 mass % and not more thanabout 45 mass % of Ni to which Cr is added in the range of at leastabout 2 mass % to not more than about 13 mass %.

While the example where the proportion of the thickness t3 of the36Ni-6Nb—Fe alloy of the low thermal expansion layer 3 to the totalthickness t1 of the high-temperature bimetal 1 is about 0.53 has beenshown in the aforementioned first embodiment, the present invention isnot restricted to this, but the proportion of the thickness of the36Ni-6Nb—Fe alloy of the low thermal expansion layer to the totalthickness of the high-temperature bimetal may be at least about 0.48 andnot more than about 0.58. According to this structure, fluctuationranges of the bending coefficients K1 and K2 in a case where theproportion of the thickness of the 36Ni-6Nb—Fe alloy is at least about0.48 and not more than about 0.58 can be suppressed to not more thanabout 3% of the bending coefficients K1 and K2 in a case where theproportion of the thickness of the 36Ni-6Nb—Fe alloy is an optimumproportion (about 0.53). The proportion of the thickness of the36Ni-6Nb—Fe alloy of the low thermal expansion layer to the totalthickness of the high-temperature bimetal is preferably larger thanabout 0.50.

While the example where the proportion of the thickness t3 of the40Ni-10Cr—Fe alloy of the low thermal expansion layer 103 to the totalthickness ti of the high-temperature bimetal 101 is about 0.55 has beenshown in the aforementioned second embodiment, the present invention isnot restricted to this, but the proportion of the thickness of the40Ni-10Cr—Fe alloy of the low thermal expansion layer to the totalthickness of the high-temperature bimetal may be at least about 0.50 andnot more than about 0.60. According to this structure, fluctuationranges of the bending coefficients K1 and K2 in a case where theproportion of the thickness of the 40Ni-10Cr—Fe alloy is at least about0.50 and not more than about 0.60 can be suppressed to not more thanabout 3% of the bending coefficients K1 and K2 in a case where theproportion of the thickness of the 40Ni-10Cr—Fe alloy is an optimumproportion (about 0.55). The proportion of the thickness of the40Ni-10Cr—Fe alloy of the low thermal expansion layer to the totalthickness of the high-temperature bimetal is preferably larger thanabout 0.50.

While the example where the lower limit of the operating temperaturerange in which the high-temperature bimetal 1 (101, 201) can be employedis about −70° C. has been shown in each of the aforementioned first tothird embodiments, the present invention is not restricted to this, butthe lower limit of the operating temperature range in which thehigh-temperature bimetal can be employed may not necessarily be about−70° C. but may be higher than about −70° C. or lower than about −70° C.

While the example of rendering the thickness t2 of the high thermalexpansion layer 2 (202) smaller than the thickness t3 of the low thermalexpansion layer 3 (103, 203) has been shown in each of theaforementioned first to third embodiments, the present invention is notrestricted to this, but the thickness of the high thermal expansionlayer may be substantially equal to or larger than the thickness of thelow thermal expansion layer.

While the example where the high-temperature bimetal 1 (101, 201) hasthe thickness t1 of about 0.2 mm has been shown in each of theaforementioned first to third embodiments, the present invention is notrestricted to this, but the thickness of the high-temperature bimetalmay be larger than about 0.2 mm or less than about 0.2 mm.

While the example where the prescribed set temperature T2 is close tothe Curie point (about 200° C., about 170° C.) of the low thermalexpansion layer 3 (103, 203) of the high-temperature bimetal 1 (101,201) and higher than the Curie point has been shown in each of theaforementioned first to third embodiments, the present invention is notrestricted to this, but the set temperature T2 may not be close to theCurie point or may not be higher than the Curie point.

1. A high-temperature bimetal comprising: a high thermal expansion layer(2) made of austenitic stainless steel; and a low thermal expansionlayer (3) made of a thermosensitive magnetic metal having a Curie pointand bonded to said high thermal expansion layer, the high-temperaturebimetal being employed over both a high temperature range of not lessthan said Curie point and a low temperature range of less than saidCurie point, wherein an upper limit of operating temperatures in saidhigh temperature range of not less than said Curie point is at least500° C.
 2. The high-temperature bimetal according to claim 1, wherein abending coefficient in said high temperature range of not less than saidCurie point is smaller than a bending coefficient in said lowtemperature range of less than said Curie point, when in use.
 3. Thehigh-temperature bimetal according to claim 1, wherein said Curie pointof said thermosensitive magnetic metal of said low thermal expansionlayer is at least 100° C. and not more than 400° C., and said upperlimit of said operating temperatures in said high temperature range ofnot less than said Curie point is at least 500° C. and not more than700° C.
 4. The high-temperature bimetal according to claim 3, wherein arange of said operating temperatures in said high temperature range ofnot less than said Curie point is larger than a range of operatingtemperatures in said low temperature range of less than said Curiepoint.
 5. The high-temperature bimetal according to claim 1, whereinsaid thermosensitive magnetic metal of said low thermal expansion layeris a Ni—Fe alloy.
 6. The high-temperature bimetal according to claim 5,wherein said thermosensitive magnetic metal of said low thermalexpansion layer is a Ni—Fe alloy containing at least 32 mass % and notmore than 45 mass % of Ni.
 7. The high-temperature bimetal according toclaim 6, wherein said thermosensitive magnetic metal of said low thermalexpansion layer is formed by adding at least one of Nb, Cr, Al, Si, andTi to said Ni—Fe alloy.
 8. The high-temperature bimetal according toclaim 7, wherein said thermosensitive magnetic metal of said low thermalexpansion layer is formed by adding at least 2 mass % and not more than8 mass % of Nb to said Ni—Fe alloy.
 9. The high-temperature bimetalaccording to claim 8, wherein said thermosensitive magnetic metal ofsaid low thermal expansion layer is formed by adding 6 mass % of Nb to aNi—Fe alloy containing 36 mass % of Ni.
 10. The high-temperature bimetalaccording to claim 8, wherein said thermosensitive magnetic metal ofsaid low thermal expansion layer is formed by adding 2 mass % of Nb to aNi—Fe alloy containing 36 mass % of Ni.
 11. The high-temperature bimetalaccording to claim 7, wherein said thermosensitive magnetic metal ofsaid low thermal expansion layer is formed by adding at least 2 mass %and not more than 13 mass % of Cr to said Ni—Fe alloy.
 12. Thehigh-temperature bimetal according to claim 11, wherein saidthermosensitive magnetic metal of said low thermal expansion layer isformed by adding 10 mass % of Cr to a Ni—Fe alloy containing 40 mass %of Ni.
 13. The high-temperature bimetal according to claim 1, wherein athickness of said low thermal expansion layer is larger than a thicknessof said high thermal expansion layer.
 14. The high-temperature bimetalaccording to claim 1, wherein a total thickness of said high thermalexpansion layer and said low thermal expansion layer increased byoxidation of said high thermal expansion layer and said low thermalexpansion layer resulting from a rise in a temperature to said upperlimit of said operating temperatures in said high temperature range ofnot less than said Curie point is not more than 1% of a total thicknessof said high thermal expansion layer and said low thermal expansionlayer before the oxidation of said high thermal expansion layer and saidlow thermal expansion layer.
 15. The high-temperature bimetal accordingto claim 14, wherein a total of mass increase per cubic centimeter ofsaid high thermal expansion layer and said low thermal expansion layerincreased by the oxidation is not more than 1.5 mg.
 16. Thehigh-temperature bimetal according to claim 1, wherein a thermalexpansion coefficient of said low thermal expansion layer in said hightemperature range of not less than said Curie point is smaller than athermal expansion coefficient of said high thermal expansion layer andlarger than a thermal expansion coefficient of said low thermalexpansion layer in said low temperature range of less than said Curiepoint.
 17. The high-temperature bimetal according to claim 16, whereinsaid thermal expansion coefficient of said low thermal expansion layerin said high temperature range of not less than said Curie point is atleast 70% and less than 100% of said thermal expansion coefficient ofsaid high thermal expansion layer.
 18. The high-temperature bimetalaccording to claim 16, wherein said thermal expansion coefficient ofsaid low thermal expansion layer in said high temperature range of notless than said Curie point is at least twice said thermal expansioncoefficient of said low thermal expansion layer in said low temperaturerange of less than said Curie point.
 19. The high-temperature bimetalaccording to claim 1, wherein a thermal expansion coefficient of saidlow thermal expansion layer in said low temperature range of less thansaid Curie point is not more than 50% of a thermal expansion coefficientof said high thermal expansion layer.
 20. The high-temperature bimetalaccording to claim 1, wherein a first end portion of said low thermalexpansion layer is fixed, and a vicinity of a second end portion of saidlow thermal expansion layer comes into contact with a fixed stoppermember (5) in said high temperature range of not less than said Curiepoint.
 21. The high-temperature bimetal according to claim 20, whereinsaid vicinity of said second end portion of said low thermal expansionlayer comes into contact with said stopper member at a temperature insaid high temperature range of not less than said Curie point and closeto said Curie point.